408 



Vertebrata. 



quite small shreds ; the very hard and thick portions of the stratum 

 corneum are not thrown off. The surface of the body is covered with 

 so-called scales, which are, however, quite different in structure 

 from those of Pish. The reptilian scutes may be termed dermal 

 warts; they are usually flattened, lie close together, and are 

 regularly arranged. In the furrows between the scales, the corneum 

 is th.in, on tlieir surface, thicker. In some cases, e.g. in Geckos and 

 others, the scales are simple round warts, granular scales. On 



l^g. 332. Longitudinal section through various scales of Eeptiles : diagrammatic. 

 A granular scales, B shield, splint scales, D do. vriih ossifications, h cuticle, s mucous 

 ayer of the epidermis, I dermis, o bony plates. — Orig, 



the head, sometimes also upon other parts of the body, there may 

 be shields, i.e., large flat plates, separated from their neighbours 

 by regular grooves. In most cases, the scale is drawn out posteriorly 

 into a point, which overlaps the one following, true scales; if 

 these are much broader than they are long, as on the ventral side of 

 the body in Snakes, they are termed splints. Not infrequently 

 the scutes are developed into longer or shorter spinose scales, 

 as iu many Ground Iguanas, and on the back of some Tree Iguanas, 

 etc. True scales have often a small median keel {e.g., in many 

 Snakes) . Occasionally, ossifications occur in the dermis ; there 

 is, for example, in each scute of the Blind- worm, a small bony plate; 

 in the Orocodilia, there are similar but larger plates in the dermis ; 

 and in the Chelonia they are very large, and often connected by 

 sutures, thus making a continuous bony shell round the animal ; 

 the boundaries do not correspond with the grooves between 

 the scutes. Skin glands are but slightly developed in the 

 Eeptilia ; there is, however, e.g, in many Lizards, a row of large 

 glands on the thigh (their openings are termed femoral pores ; or, in 

 front of the anus, pre-anal pores) ; in the Orocodilia also, and in many 

 Chelonia, large isolated skin glands occur. The digits, in contra- 

 distinction to those of the Amphibia, are provided with claws, 

 peculiar borny structures, covering the last phalanx like a cap ; 

 they are not affected by the ecdysis; they grow gradually from 

 within, and are simultaneously worn away at the surface. 



